fe_op_bind_success()

What, if anything, are the differences between fe_op_bind_success() and an
(OpenLDAP 2.3 compatible) on_response that checks if (op->o_tag ==
LDAP_REQ_BIND && rs->sr_err == LDAP_SUCCESS)? Is it possible to have a
bind without a response? Are fe_* global only, or can they be
per-database? etc...